It is increasingly common for data to be distributed to users from a central source. It is often desirable in such situations to protect the information transmitted in such a way that it can only be used by the intended recipients. Classic examples might include the distribution of “pay TV” video data via radio communications, or more recently over IP networks such as the internet or a cellular telephone network. Several references seeking to address these problems are discussed below.
U.S. Pat. No. 6,714,649 discloses a method and system for broadcasting programs in a network and for blocking illegal access to the broadcast programs. The system comprises a central station and a subscriber terminal. Data of a program to be broadcasted is first scrambled with a scramble key. The scramble key is updated in a short period of time. The scramble key is encrypted with a first key, the first key being assigned to the subscribed terminal. The first key is encrypted with another master key. The master key is set inside the subscriber terminal. After the program is downloaded in the subscriber terminal, the encrypted first key is decrypted by using the master key set in the subscriber terminal. If the program stored in the subscriber terminal is to be executed, the encrypted scramble key is decrypted by using the first key and the scrambled data of the program is unscrambled with the decrypted scramble key. Further like the scramble key, the first key is updated periodically.
U.S. Pat. No. 6,987,854 discloses a method and system for recording encrypted digital data. The system comprises a transmitter, decoder and a portable support device. The digital data is scrambled using a control word. The control word is encrypted with a first key. The scrambled data is transmitted together with the first key-encrypted control word. The first key-encrypted control word is received and decrypted with a decoder that includes an equivalent of the first key. The control word is re-encrypted with a second key which is stored in the portable support device for further secured redistribution. The re-encrypted control word and the scrambled digital data are recorded on a digital recording medium.
U.S. Pat. No. 6,091,818 discloses a method for sending encrypted messages in a conditional access system. The services supplied by a service provider in a conditional access system consist of an item scrambled by control words. The control words are encrypted with an encryption algorithm with a key K and are supplied in messages by which the control words are kept secret. Further, the same message may contain the same control word encrypted several times with a different encryption key. The encryption keys are chosen at random.
U.S. RE 38529 discloses a method of transmitting data through a broadcast system. The method comprises assembling news data and encrypting the news data with a first encryption key. Further, each news data is encrypted with a different first encryption key. The encrypted news data is further encrypted with a common second encryption key. The twice-encrypted news data is then transmitted to a receiver. Upon reception, the twice-encrypted news data is decoded by using second encryption key. As a result the encrypted news data is yielded which is decrypted using the first encryption key used to encode news data prior to transmission.